This disclosure describes a filter construction or structure for filtering a particulate from fluids including a gas or a liquid. More particularly, this disclosure relates to a bag house filter element. Filter elements are used in a bag house to remove entrained particulates typically from gaseous effluents. Bag house filter structures are typically used to treat large volumes of gaseous effluents to remove dust and grit. The invention further relates to filter assemblies, structures and methods. More particularly, the present invention relates to cabinet filter assemblies wherein the filter element includes a series of bags suspended within a cabinet for filtering dust or other particulates from the gaseous effluent. The bags useful in a dust cabinet of the invention can comprise a variety of the structural shapes or configurations. The bag for the filtration element for the cabinet of the invention obtains high filtration efficiency combined with extended lifetime. Bags can comprise filter tubes or sheet-like filter structures with a folded symmetry. Filter housings can contain a large but varied number of bag units depending on the volume of air filtered.
Dust collectors, also known as bag houses, are generally used to filter particulate material from industrial effluent or off gas. Once filtered, the cleaned off gas can be vented to the atmosphere or recycled. Such a bag house dust collector structure generally includes one or more flexible filter banks supported within a cabinet or similar structure. In such a filter cabinet and bank, the filter bag is generally secured within the cabinet and maintained in a position such that effluent can efficiently passes through the bag efficiently removing entrained particulates. The filter bag, secured within the cabinet, is typically supported by a structure that maintains the clean airside separate from the dirty airside and supports the filter bag to maintain efficient operation.
We have found that the efficiency of a bag house element can be maintained or improved and that the overall lifetime of the bag house element can be substantially maintained and improved using a layer of fine fiber (fiber having a maximum dimension of about 0.5 microns) on the bag house element. During filtering operations, particulates that encounter the bag house element are stopped by and are maintained on or in the surface of the filter structure. The buildup of these particulate materials on the surface of the filter can at some point begin to reduce filter life and efficiency of particulate removal. By placing a portion of the fine fiber on opposing sides of the filter element, we have found that the efficiency of the filter is maintained while the lifetime of the filter is substantially increased. A reverse pulse clean step can be used to remove the accumulated particulate and substantially reduce pressure drop.
We have found that the bag houses structures of the invention can take at least two embodiments. In a first embodiment, the fine fiber filter structure can take the form of a porous tubular layer on a tubular bag or member with a sealed end with the fine fiber formed on the surface on which the particulate impacts the bag. The open end of the tubular member can be fitted with a collar encircling the tubular member. The collar can be incorporated in a seal between the tubular member and support structure in a bag house structure. The tubular member can be supported by a support member that can maintain the shape of the bag and prevent collapse. Such members can comprise a variety of structures including a perforated tube or wire mesh.
In a second embodiment, the fine fiber structure can take the form of a porous filter layer on a bag formed from generally rectangular fabric panels that are connected or sealed along opposite edges or seams to separate clean side from a dirty or dusty side. In a preferred embodiment a single generally rectangular elongated strip fabric is folded along a bisecting lower edge forming a folded structure with the fine fiber formed on the surface on which the particulate impacts the bag. A substantially U-shaped metal clip can extend along of the lower edge of each bag and sides of the shim member or clipped together to clamp the lower edge of the bag therebetween. The purpose of this member is to provide sufficient weight at the lower edge of the bag to maintain it in the vertical position and to prevent portions of the bag being drawn upwardly by the effect of the gas passing through the bag and the differential pressures therein. A wire mesh or other suitable materials is enclosed within the interior of the bags to prevent the panels from collapsing and to ensure that the surface of each bag is subject to gas transfer. A collar is positioned on the upper surface or end of each bag. Such a collar is used to ensure that the bag is sealed to the cabinet for proper and efficient filtering operations. In this application the term xe2x80x9cunchanged for filtration purposesxe2x80x9d refers to maintaining sufficient efficiency to remove particulate from the fluid stream as is necessary for the selected application.
The invention also relates to polymer materials that can be manufactured with improved environmental stability to heat, humidity, reactive materials and mechanical stress. Such materials can be used in the formation of fine fibers such as microfibers and nanofiber materials with improved stability and strength. As the size of fiber is reduced the survivability of the materials is increasingly more of a problem. Such fine fibers are useful in a variety of applications. In one application, filter structures can be prepared using this fine fiber technology. The invention relates to polymers, polymeric composition, fiber, filters, filter constructions, and methods of filtering. Applications of the invention particularly concern filtering of particles from fluid streams, for example from air streams and liquid (e.g. non-aqueous and aqueous) streams. The techniques described concern structures having one or more layers of fine fibers in the filter media. The compositions and fiber sizes are selected for a combination of properties and survivability.